Method of manufacturing a luminescent screen of a color television display tube

ABSTRACT

A METHOD OF MANUFACTURING A LUMINESCENT SCREEN OF A CATHODE-RAY TUBE FOR DISPLAYING COLORED PICTURES. THE LUMINESCENT AREAS OF THE SCREEN ARE SEPARATED BY LIGHT ABSORBING AREAS. THE LUMINESCENT AREAS ARE APPLIED BY MEANS OF ANY METHOD PREVIOUS TO THE APPLICATION OF THE LIGHT ABSORBING AREAS WHICH ARE APPLIED BY MENS OF ELECTROSTATIC DEPOSITION. FOR THE ELECTROSTATIC DEPOSITION OF THE LIGHT ABSORBING AREAS A CONDUCTIVE LAYER AND A DIELECTRIC LAYER ARE FORMED IN THE INTERMEDIATE SPACES BETWEEN THE LUMINESCENT AREAS. THE LAYERS ARE FORMED BY MEANS OF RINSING WITH DILUTE, I.E., LOW VISCOSITY, SOLUTIONS BY WHICH THE FORMATION OF THE LAYERS ON THE LUMINESCENT AREAS IS IMPEDED.

June 1974 N. E. F. HANSEN ETAL METHOD OF MANUFACTURING A LUMINESCENTSCREEN OF A COLQR TELEVISION DISPLAY TUBE Filed Sept. 21, 1971 INVENTORSNORBERT E. F. HANSEN WALTER F. K. LITT MANN United States Patent US. Cl.117-211 9 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing aluminescent screen of a cathode-ray tube for displaying coloredpictures. The luminescent areas of the screen are separated by lightabsorbing areas. The luminescent areas are applied by means of anymethod previous to the application of the light absorbing areas whichare applied by means of electrostatic deposition. For the electrostaticdeposition of the light absorbing areas a conductive layer and adielectric layer are formed in the intermediate spaces between theluminescent areas. The layers are formed by means of rinsing withdilute, i.e., low viscosity, solutions by which the formation of thelayers on the luminescent areas is impeded.

The invention relates to a method of manufacturing a luminescent screenof a cathode-ray tube for displaying colored pictures comprisingdiscrete areas of materials which upon excitation by electrons luminescein different colors, the luminescent areas being separated bylightabsorbing material. The luminescent materials are first provided onthe window of the tube by means of a photosensitive binder and thelight-absorbing material is provided afterwards.

A screen constructed in this manner provides the advantage that with thesame contrast the tinting of the Window glass may be omitted or be atleast smaller. As a result of this the observed brightness of thepicture is greater.

US. Pat. No. 3,365,292 describes a method of manufacturing such ascreen. After the various luminescent materials have been provided onthe window by means of a photosensitive binder, they are provided with afilter layer. The window, which is provided with the surface regions ofthe various luminescent materials, is then covered with a photosensitivebinder. The photosensitive binder is soluble in a solvent but afterexposure to a certain radiation which is not passed by the filter layer,the binder becomes insoluble in the relevant solvent. The layer ofbinder comprises a material which does not or only slightly absorbs therelevant radiation and which can be converted into a darklight-absorbing material. After drying the layer of binder it is exposedto the relevant radiation through the window. Since the filter layer ispresent on the surface elements which are covered with surface regionsof the various luminescent materials, the

binder layer is prevented from adhering in these places.'

The binder is hardened in all the free surface regions of the window.-After dissolving the non-hardened binder the material present in thehardened layer of binder is converted into a dark light-absorbingmaterial by heating.

The difiiculty of this method is that a large number of operations arenecessary.

US. Pat. No. 3,475,169 discloses a method of manufacturing a luminescentscreen of a cathode-ray tube for displaying colored pictures whichcomprises in discrete surfaces substances which upon excitation byelectrons "ice luminesce in different colors, said surfaces beingseparated by surfaces of a light-absorbing material. In this method thesurfaces of the various luminescent materials and of the light-absorbingmaterial are provided electrophotographically, in which for theformation of the charge image for the light-absorbing material aradiation is necessary. Also described in this patent specification is amethod in which the surfaces of the various luminescent materials areprovided electrophotographically but in which a binder is added to theluminescent materials which is modified in a further manufacturing stepso that in the subsequent charging for the light-absorbing material itwill not absorb any charge. In all these methods the window is entirelyprovided with a conductive layer and a photoconductive layer.

According to the invention, a conductive layer is provided, by rinsingwith a low viscosity solution, i.e., one having a maximum concentrationof about 10%, on the window which comprises the discrete surfaces of thevarious luminescent materials, the conductive layer being formed only inthe intermediate spaces located between the luminescent areas, adielectric layer being then provided on the conductive layer by means ofrinsing with a maximum 10% solution, the dielectric layer then beingdried and charged by means of a corona discharge, and thelight-absorbing material being provided on the charged dielectric layerby means of electrostatic deposition from a suspension in an apolarsolvent. In this method the light-absorbing material is provided onparts of the window which are still uncovered after providing theluminescent materials. Because of the low viscosity of the solutionhaving a maximum concentration of 10% the porous structure of theluminescent dots prevents the formation of a coherent conductive layerin the region of the luminescent dots so that the conductive layer isactually formed only in the intermediate spaces between the luminescentdots. The formation of a coherent dielectric layer on the luminescentdots is strongly impeded by the structure of the luminescent dots sothat the di electric layer is present only on the conductive layer. Thedielectric layer after drying should preferably have a thickness of lessthan 10 ,um., in particular from l5 m.

During charging, the dielectric layer is charged to a high chargedensity as a result of its large capacity. Owing to the absence of acapacitive layer structure there is no charge on the luminescent dots.The formed charge image in the intermediate spaces is pigmented by meansof an electrostatic deposition from a suspension of the blackpigmentation agent in an apolar solvent. An apolar solvent must be usedin order that the charge image be not discharged in contact with thesolvent. According to this method in which only three treatments with aliquid are effected without irradiation a readily covering blackpigmentation of the intermediate spaces between luminescent dots of anysize is obtained without a disturbing deposition of the blackpigmentation agent on the luminescent dots occurring.

The invention furthermore relates to a cathode-ray tube comprising aluminescent screen manufactured by this method.

In order that the invention may readily be carried into effect, it willnow be described in greater detail, by way of example, with reference tothe accompanying drawing, the sole figure of which shows a part of awindow of a tube during the manufacture. The inside of the window of ashadowmask tube is provided with green, blue and red luminescentphosphor dots. In every case the inside of the window and the possiblyalready provided luminescent dots for producting a certain color arecovered with a suspension of a relevant luminescent material (forproducing another color) in a polyvinyl alcohol solution to whichammoniumdichromate has been added. After drying the layer, during anexposure to ultraviolet radiathe photo-hardening, the swelling powder ofthe layer in the exposed places is reduced and the excessive material isthen washed away. A conductive layer is first provided on the windowcomprising the luminescent dots which layer is formed only in theintermediate spaces between the luminescent dots. This is achieved byrinsing with dilute solutions of ionogenic materials in polar andnonpolar solvents, possibly with the addition of wetting agents. Theconductive layer which in a subsequent manufacturing step serves as anopposite electrode should have only a minimum conductivity because onlyvery small currents must flow through the conductive layer. For example,0.5 to 3% solutions of potassium silicate in Water or a mixture ofpolyvinylalcohol and glycerine in water are successfully used. Othersubstances for manufacturing said conductive layer may be used by thoseskilled in the art. On said conductive layer a dielectric layer ofapproximately 1-5 am. thickness is provided. For that purpose the insideof the window is treated, for example, with a 15% solution ofpolyvinyl-carbazol in parts of chlorobenzene and 1 part ofdichloromethane. Instead of the polyvinylcarbazol may be used a varietyof organic film-forming polymers having good dielectric properties. Inthe places of the luminescent dots the formation of a coherent layer isagain strongly impeded. The layer is then dried. The figure shows theresulting structure. Luminescent dots 2 are present on a window 1. Theintermediate spaces of the window 1 are provided with a conductive layer3 on which a dielectric layer 4 is present. The picture screen is nowexposed to a positive or negative corona discharge. One or severalneedleshaped tips or thin wires are connected to a high-voltage sourceof 6-30 kv. direct voltage and guided over the grounded layer 3 at adistance of a few centimeters therefrom. The dielectric layer 4 ischarged to a high charge density in the intermediate spaces as a resultof its large capacity and the counter charges are present in theconductive layer 3. No charge occurs on the luminescent dots owing tothe lacking capacity. This charge image in the intermediate spaces isnow pigmented by means of an electrostatic deposition from a suspensionof a black pigmentation agent and an apolar solvent. Any black, finelydivided dye may be used as a black pigmentation agent. A suitableprescription for a positively charged pigmentation agent for the blackmatrix is as follows:

Black pigmentation agent Bayer 7454 Ca 30 Polymetacrylate SV 46 .Rohmund Haas 5 Ca-diisopropylsalicylate 0.01 Ca-dodecylsulfosuccinate 0.01

Other black pigmentation agents, for example, soot may be used in asimilar manner. By using other ionogenic materials, negative charges ofthe pigmentation agents can also easily be reached for the case in whicha positive charge of the dielectric layer is to be used.

What is claimed is: 1. A method of manufacturing a luminescent screenfor a color display cathode ray tube, said screen comprising atransparent substrate and discrete areas of electronexcitable colorluminescent materials disposed thereon and separated by a lightabsorbing material, said method comprising the steps of:

(a) providing a structure comprising said substrate and said discreteluminescent areas located directly on a first face thereof;

(b) forming at only exposed regions of said first face a conductivelayer such that said discrete luminescent areas are substantiallycompletely surrounded there- (c) forming at only said conductive layer alayer of dielectric material;

(d) charging said dielectric layer by corona discharge;

and

(e) electrostatically depositing said light-absorbing material on saidcharged dielectric layer.

2. A method of manufacturing a luminescent screen for a color displaycathode ray tube, said screen comprising a transparent substrate anddiscrete areas of electronexcitable color luminescent materials disposedthereon and separated by a light absorbing material, said methodcomprising the steps of:

(a) providing a structure comprising said substrate and said discreteluminescent areas located directly on a first face of said substrate;

(b) rinsing exposed regions of said first face with a low viscositysolution of an ionogenic material carried in a medium of at least one ofa polar and an apolar solvent, thereby forming a conductive layer atonly said exposed regions surrounding said discrete luminescent areas;

(0) rinsing said conductive layer with a low viscosity solution of adielectric material, thereby forming a layer of dielectric material atonly said conductive layer, said conductive and dielectric layerssubstantially completely surrounding said discrete luminescent areas andbeing only laterally disposed with respect to said discrete areas;

((1) charging said dielectric layer by corona discharge;

and

(e) electrostatically depositing said light-absorbing material on saidcharged dielectric layer.

3. A method as recited in claim 2, wherein the thickness of saiddielectric layer is less than about 10 microns.

4. A method as recited in claim 2, wherein each one of said first andsecond solutions has a concentration of said ionogenic material and saiddielectric material, respectively, not exceeding 10%.

5. A method as recited in claim 2, wherein said first solution furthercomprises a wetting agent.

6. A method as recited in claim 2, wherein said first solution is anaqueous solution of potassium silicate.

7. A method as recited in claim 2, wherein said first solution is anaqueous solution of polyvinyl alcohol and glycerine.

8. A method as recited in claim 2, wherein said second solution consistsessentially of polyvinyl carbazol, chlorobenzene, and dichloromethane.

9. A method as recited in claim 2, wherein said second solution consistsessentially of dielectric film forming polymer, chlorobenzene, anddichloromethane.

References Cited UNITED STATES PATENTS 3,113,037 12/1963 Watanabe1l793.4 R 3,206,323 9/1965 Miller et al. 117- 93.4 R 3,108,893 10/1963Oliphant 11793.4 R. 3,251,551 5/1966 Walberg 117-93.4 R 3,365,292 l/l968Fiore et al. 96-32.6 3,475,169 10/1969 Lange 117335 CM 2,682,478 6/ 1954Howse 11733.5 CM 2,787,556 4/1957 Haas l1733.5 CM 3,593,678 7/1971Miller 11733.5 CM

WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US.Cl. X.R.

96l, 1.2, 2.5, 36.2; 11717.5, 33.5 C, CM, 37, 93.4 A, 212, 215, 218,219; 33-92 P0405) UNITED STATES PATENT OFFICE I CERTIFICATE OFCORRECTION Patent No. 3,814,629 Dated J uge 4, 1974 In nt r(s) NORBERTE. F. HANSEN ET AL It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 3, line 49, after "30" insert --g--;

line 50, after "5" insert --g-- line 51, after "0.01" insert --g-;

line 52;, after "0.01" insert -g--.

Signed and sealed this 8th day of October 1974.

(SEAL) Attest:

' MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

